The present invention relates to a back projection type video display device in which an optical image is projected from a screen back side by a projection unit for projecting the optical image in response to a video signal, and a back reflective mirror for use in the device. The back reflective mirror changes an optical path of a projected video light in a screen direction. For the back reflective mirror of the present invention, the reflective surface is formed of a metal thin film, and a topcoat is formed of a colorless/transparent resin on the surface of the metal thin film for protection of the surface.
For a reflective mirror (hereinafter referred to as the back mirror) for use in a back projection type video display device for projection onto a screen from a back side to change an optical path of a projected video light in a screen direction, a mirror described, for example, in JP-A-2001-235798 is known. That is, a reflective film of aluminum (Al) is formed on a glass substrate by vacuum evaporation or vacuum sputtering which is a vacuum film forming process, and an amplified reflective film having a film thickness of 0.2 to 0.3 μm is formed of a transparent inorganic material on the reflective film by the vacuum evaporation. This glass mirror is superior in smoothness, reliability of resistance to environment and the like.
However, the back mirror for use in the back projection type video display device has a large size, a film forming device (e.g., sputtering device) for forming the reflective film is expensive, and makers capable of manufacturing the device are limited. Since an operation efficiency in forming the film by the vacuum evaporation, value sputtering or the like is low, a price of the back mirror is high.
On the other hand, in recent years, for example, a back mirror low in manufacturing cost has been used, including a film on which a reflective layer is formed, and the film is extended via a metal frame. The film-formed back mirror described, for example, in JP-A-9-311207 and shown in FIG. 2 is known. In this mirror, a metal thin film (Ag) is deposited on a film of a resin (PET), and a topcoat is formed of a colorless/transparent resin on the surface of the film. The Ag reflective film is formed by use of evaporation in the same manner as in the glass substrate, but a rolled film is used and wound up to form the film by the film forming device, and therefore there is an advantage that the film can be formed at a low cost.
As a film forming method of the reflective film, in addition to the above-described vacuum film forming method (vacuum evaporation method, value sputtering method), a spraying method described, for example, in JP-A-2001-295059 is known. In this method, a solution containing a metal salt and a reducer-containing solution are sprayed with respect to a material to be plated so that the material is plated. When this method is used, the expensive value film forming device (equipment) is not required, and therefore there is an advantage that the film can be formed at the low cost.